Ion irradiation of amorphous hydrogenated silicon carbide films introduces
additional disorder into the films and leads to chemical modifications. The
se effects were monitored using Infrared, UV-visible optical and Raman spec
troscopies. Samples were prepared by plasma enhanced chemical vapour deposi
tion (PECVD), then irradiated with 300 keV Ar+ to fluences ranging from 5 x
10(13) to 1 x 10(15) cm(-2). The hydrogen concentration was determined by
elastic recoil detection analysis using 2.0 MeV He+ beam.
After ion irradiation, the absorption coefficient in the UV-visible energy
range was observed to increase by an order of magnitude, while the optical
energy gay decreases from 3.2 eV to 2.0 eV. These changes are due to the fo
rmation of carbon clusters, as evidenced by the carbon yield in Raman measu
rements. Infrared spectra indicate that this excess of carbon atoms results
from the breaking of CH, bonds in the as-grown film and by a concomitant d
ecrease in the hydrogen concentration. In addition, defects created by ion
bombardment change the oscillator strength of the Si-H vibrational modes. (
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